Multiply and let rip, perhaps (6)
I believe the answer is:
triple
'multiply' is the definition.
(tripling is a kind of multiplying)
'let rip perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'let'+'rip'='letrip'
'letrip' is an anagram of 'TRIPLE'.
'and' acts as a link.
(Other definitions for triple that I've seen before include "Three times" , "involving several parties" , "make much longer" , "Multiply by three" , "In three parts" .)